My number one isn't technically a Halloween song but it creeps me out and I have to play it every Halloween. In the Room Where You Sleep by Dead Man's Bones. There is just something haunting about Ryan Gosling's voice and the lyrics are just unsettling.
My number two has to be I Put a Spell on You. The best versions hands down are Screamin' Jay Hawkins and Credence Clearwater Revival.
I have a 70 song playlist on my ipod of just creepy Halloween songs that is on constant rotation all the time.
I would add the YouTube videos but I'm on my phone, I'll post the videos when I get on my laptop later.